1. Technical Field
The present invention relates to a resolver and a multiple-rotation detector which comprises a plurality of resolvers.
2. Related Art
A resolver includes a rotor which rotates together with a shaft and a stator which is located around the rotor. The rotor is shaped like an eccentric disc, an ellipse, or the like in which a distance between the rotation center of the rotor and the surface thereof is different depending on an angular position thereof. Accordingly, when the rotor rotates, a gap between the rotor and the stator is changed at a certain fixed position on the stator. The stator includes a detector which detects this gap. The detector includes a coil, detects the change of a magnetic flux density caused by the change of a gap between the rotor and the stator, and measures the gap.
A single resolver can detect an angular position of a shaft, on which the rotor is mounted, through one rotation, but cannot detect an angular position (an absolute angular position) thereof through a plurality of rotations. A multiple-rotation detector which detects an angular position through a plurality of rotations is known. The multiple-rotation detector comprises a shaft, a single or a plurality of speed-reduced rotational element/elements in which the rotational speed of this shaft is reduced, and a resolver which can detect a rotation angle of this speed-reduced rotational element during one rotation. As a result, the multiple-rotation detector can detect the angular position of the shaft over a plurality of rotations, for example, hundreds of rotations.
FIG. 1 is a cross-sectional view perpendicular to an axis of reluctance resolvers of a multiple-rotation detector of a conventional example. FIG. 2 is a cross-sectional view taken along the portion A-A illustrated in FIG. 1. FIG. 3 is a cross-sectional view taken along the portion B-B illustrated in FIG. 1.
A reluctance resolver in FIG. 1 has three resolvers which are located on the same plane. The rotation centers of rotors 32, 27, 25 of the respective resolvers are located so that the rotation centers thereof are positioned at respective vertexes of an isosceles triangle. Additionally, four teeth 1 to 4 are provided on the periphery of the rotor 32, four teeth 5 to 8 are provided on the periphery of the rotor 27, and four teeth 9 to 12 are provided on the periphery of the rotor 25, respectively. An excitation winding and a detection winding are wound around each of these teeth via a bobbin, and the windings are electrically connected to respective pins of a connector 14. Further, the connector 14 is electrically connected to an unillustrated connector in a signal processing circuit. The teeth 1 to 12 are supported on a stator 66 and the stator 66 is supported on a casing 16 via a spacer 17 and a casing 19 via a spacer 18. The rotors 32, 27, 25 and the stator 66 are formed of a magnetic material. An input shaft 31 is supported on the casing 16 via a bearing 40 and on the casing 19 via a bearing 45. A gear 34, which is formed of a non-magnetic material, and the rotor 32 are fitted to the input shaft 31. A shaft 13 is supported on the casing 16 via a bearing 41 and on the casing 19 via a bearing 42. A gear 30 formed of a non-magnetic material and a gear 15 formed of a non-magnetic material are fitted to the shaft 13. A gear 54 formed of a non-magnetic material and the rotor 27 are mounted to a shaft 21 via a bearing 28. A gear 50 formed of a non-magnetic material and the rotor 25 are mounted to a shaft 22 via a bearing 26.
A speed-reduction gear mechanism is formed by engagement of the gear 34 and the gear 30, engagement of the gear 15 and the gear 54, and engagement of the gear 15 and the gear 50. The gear 54 is adhered to the rotor 27 and the gear 50 is adhered to the rotor 25. In accordance with the above-described speed-reduction mechanism, when the input shaft 31 makes 24 rotations, the rotor 27 makes one rotation, and when the input shaft 31 makes 25 rotations, the rotor 25 makes one rotation.
By applying a pulse voltage between the pins for excitation of the connector 14, a voltage corresponding to an angular position of the rotor is generated between the pins for detection of the connector 14. The angular position of the rotor of each of the resolvers can be calculated by performing an interpolation operation of this voltage. An absolute angular position of the input shaft 31 within one rotation can be detected at the resolver which comprises the teeth 1 to 4 and the rotor 32. An absolute angular position of the input shaft 31 within 25 rotations can be detected at the resolve which comprises the teeth 5 to 8 and the rotor 27. An absolute angular position of the input shaft 31 within 24 rotations can be detected at the resolver which comprises the teeth 9 to 12 and the rotor 25. Further, by numerically processing the detected values of the three absolute positions of these three resolvers, the position of the input shaft 31 up to 600 rotations can be detected with a high degree of accuracy.
In the aforementioned conventional resolver and multiple-rotation detector, one phase of the resolver is formed of one tooth. Consequently, the resolver and the multiple-rotation detector are easily subjected to the influence of magnetic field noise from outside. Therefore, it is necessary to move away from a noise source, dispose a magnetic shield at the exterior of the detector, or the like.
FIG. 4 is an enlarged view of the periphery of the rotor 32 in FIG. 1. A magnetic flux which is excited to detect a rotor angular position is shown by a line 68 in FIG. 4. Hereinafter, this excited magnetic flux will be referred to as a magnetic flux 68. The magnetic flux 68 comes out of the tooth 1, passes through the interior of the rotor 32, the tooth 2 or the tooth 4, the interior of a tooth supporting member of the stator 66, and returns to the tooth 1. A magnetic flux line which comes out of the tooth 3 similarly passes through the interior of the rotor 32, the tooth 2 or the tooth 4, the interior of a tooth supporting member of the stator 66, and returns to the tooth 3. When a magnetic flux 67 generated by magnetic field noise enters the stator 66 from outside, the noise magnetic flux 67 and the magnetic flux 68 which is used to detect the rotor angular position magnetically interfere with each other within the tooth supporting member. As a result, an error occurs at the calculated absolute angular position. Moreover, in a case where a plurality of resolvers are disposed on the same plane, an amount of magnetic interference is changed and complicated depending on entering directions of the noise magnetic flux, making the correction difficult.